About 2 years ago my step daughter moved in with us. We were not sure how this was all going to work out so we asked "the mom" to simply pay for clothes she needs and reimburse us on the child support being garnished from husbands pay. Now that this is not going as well as we'd hoped and step daughter is here to stay we would like to get the garnishment stopped and possibly arrange for some support from "the mom". Do we have to go to court to do either part of this.

Yes. Until there is formal paperwork awarding him custody and showing him as custodial parent. The "mom" can come get the child at any time and he is still responsible for child support.
This should have been taken care of 2 years ago.

Until the Judge signs the Order stopping this child support it will continue. Have this taken care of as soon as possible. You can discuss with your attorney the possibility of having the mother return some of the money that was paid in the 2 years that the child lived with you. You may just get some of it returned. Doesn't hurt to ask the Judge.

Yes in fact the mother did not have to "give you back" any child support, she could have legally kept it until you went back to court and the judge ruled.

I paid for almost 3 years before we got a court to issue a final ruling to stop supprt payments ( even with kids living with me)

You need to hope mom does not find out or sue may try and sue you for all that money back